Electric motor truck control



1963 F. J. SCHENKELBERGER 3,114,871

ELECTRIC MOTOR TRUCK CONTROL Filed May 21, 1958 3 Sheets-Sheet 1 FIG! 13INVENTOR.

FRANK J. SCHENKELBERGER ATTYS.

1963 F. J. SCHENKELBERGER 3,114,371

ELECTRIC MOTOR TRUCK CONTROL Filed May 21, 1958 5 Sheets-Sheet 2 HI n3no INVENTOR.

FRANK J. SCHENKELBERGER ATTYS.

Dec. 17, 1963 F. J. SCHENKELBERGER 3,114,871

ELECTRIC MOTOR TRUCK CONTROL Filed May 21, 1958 3 Sheets-Sheet 3 A MM\VI 138 y $2 HMMMMMMMMM INVENTOR.

FRANK J. SCHENKELBERGER ATTYS.

This invention relates to control systems for electric motors and moreparticularly to improved hydraulic means for operating a variableresistor in a control circuit for an electiric drive motor as employed,for example, in electrically powdered industrial lift trucks, or likevehicles.

in brief, my invention contemplates converting force applied to a footoperated accelerator pedal into hydraulic pressure by means of asuitable mechanical linkage system to operate a master hydraulic pistonand cyliinder of a closed hydraulic control system. The hydraulic force,so obtained, preferably is applied in one of two manners, depending onthe functional result desired, to operate a carbon pile resistor whichregulates the flow of current to the motor to be controlled. The carbonpile resistor is infinitely variable and composed of a series of carbondiscs arranged so that the tighter the discs are squeezed together, thelower resistance they present to the flow of electricity; thusproviding, within limits, an infinitely variable rheostat for varyingthe rotational speed of the drive motor. In the normal operation of myhydraulic control system, the force of the hydraulic pressure is appliedto one end of the stationary carbon pile resistor, thus to vary itsresistance and the motors acceleration. When maximum compression of thecarbon pile is attained, a means for automatically bypassing the same isavailable to effect high speed operation of the motor. Such infinitevariable control of the motors speed and vehicles acceleration is alsoavailable for deceleration by utilizing the hydraulic pressure forvarying the resistance of the carbon pile in applying reverse torquebraking to the motor. Certain electrical and mechanical interlock meansare embodied with the control system to prevent full current pluggingand to prevent energization of the vehicles drive motor unless theoperators seat of the vehicle is occupied.

The main object of my invention is to provide a new and improved controlsystem for regulating the operation of an electric motor.

Still another object of my invention is to provide a new and improvedspeed control system for an electric motor used in driving a materialshandling vehicle, whereby the vehicle may be operated at infinitelyvariable rates of acceleration and deceleration.

Another object of my invention is to provide a hydraulic system forcontrolling the operation of an electric motor.

A further object of my invention is to provide a control system, asaforesaid, which employs hydraulic pressure for varying the compressionof a carbon pile rheostat controlng the energization of an electricdrive motor in circuit therewith.

A still further object of my invention is to provide a means forcontrollin the operation of an electric drive motor and for acceleratingthe motor at a uniform rate in accordance with a predetermined rate offlow of hydraulic fluid.

mother important object of my invention is to provide a hydraulic systemincluding an accumulator for controlling the operation of an electricmotor, the accumulator performing as an actuator in certain instances tocontrol operation of the motor.

An additional object of my invention is to provide an improved controlsystem, as aforesaid, which embodies suitable mechanical and electricalinterlock means to prevent both initial energization of the electricmotor and reversals in the direction of current flow to such motor, whennited States Patent ice the operating circuit therefor is conditionedfor a high rate of current flow.

A still further object of my invention is to provide a new and improvedhydraulic control for operating a variable resistance regulatory of theoperating speed of an electric motor and to provide for controlledreverse torque braking of the motor.

The above and further objects, features, and advantages of thisinvention will occur to those familiar with the art from the followingdetailed description and specifications of a preferred embodiment of theinvention, as illustrated in the accompanying drawings.

in the drawings:

FIGURE 1 is a side eleva-tional view of an industrial lift truck withwhich the control system of the present invention is embodied;

FIGURE 2 is a schematic diagram of the electrical circuit for operatingthe material handling vehicle of P16- URE 1;

FIGURE 3 is a perspective view schematically illustrating thearrangement of the hydraulic control system for regulating the carbonpile resistor unit used in the electric motor circuit of Fl'GURE 2; and

FIGURE 4 is a cross-sectional view of the hydraulic actuator employed inthe hydraulic control system of FIGURE 3 and illustrating certaindetailed features of its construction.

Although the control system of the present invention is intended for usewith commercial vehicles of various types, by way of example, it will bedescribed hereinafter as it relates to an industrial fork lift truck itillustrated in FlGURE 1. Vehicle ill comprises a main frame 11 supportedby a pair of ground engaging drive wheels 12 located adjacent theforward end thereof and a pair of ground engaging steering wheels 13adjacent its rear end. The rear wheel 13 are controlled in theirsteering movement by conventional linkage operated by a hand steeringwheel El i mounted in the upper end of a steering column 15 forwardly ofan operators seat 16. At the forward end of the truck frame Iii is agenerally vertically extending tilting mast it? which carries aload-supporting fork assembly 18, the latter being movable verticallyalong the mast 17. A counterweight 19 at the rear end of the truck isnormally employed, as illustrated, to counteract the overturning momentimposed by a load on the fork assembly 18. Truck id is conventionallydriven by a battery powered electrical drive motor Ztl which isoperatively coupled to drive wheels 12 by means of a conventional torquetransmitting means (not illustrated).

The drive motor 2ft, together with the electrical control and powercircuits therefor, is shown schematically in FIGURE 2 of the drawingsand includes a field winding 21 and an armature 22. T he components ofthe drive motor major control circuit include a directional selectorswitch 23 having a lever operated direction selector switch blade 24-movable from a neutral position to either a forward direction circuitcontact 25 or a reverse direction circuit contact Switch 23 is connectedto one side of a battery supply 3t over supply conductor 31 and any oneof three sets of contacts 32, 33, or 34 associated, respectively, withconductors 35, 36, and 37. (Contacts 33, related to a firstnicro-switch, are normally closed while contacts 32 and 34 are normallyopen.

The switch blade 24, when engaged with the forward direction contact 25closes circuit between conductor 36 having closed contacts 33 and abranch conductor 38 to energize a forward direction relay coil 39. In alike manner, closing switch blade 24 with the reverse direction contact26 connects branch conductor 4d and relay coil ll in circuit withconductor 36 and the normally closed contacts 3-3. The two branchconductors Ell and do are joined to the other side of the battery andline 33 conductor 42 over conductor and a dead man scat interlock switch44.

Energizing the forward direcion relay coil 39 serves to close contactset 32, while energizing the reverse direction relay coil 41correspondingly serves to close contact set 34; both instan esestablishing a hold circuit v inch continues to control the motor afterthe micro-switch contacts 33 are opened, as will appear presently.

The armature 22 of the drive motor 29 is powered in series circuit withan interlocked set of normally closed reverse direction contacts andnormally open reverse direction contacts Sit of branch conductor 52. Thearmature is also in series with a second interlocked set of normallyclosed forward direction contacts 53 and normally open forward directioncontacts 54 in a second branch conductor 55; contacts 5i) and 51 beingoperated by relay coil 41 and contacts $3 and 54 being operated by relaycoil The field coil 21 of the drive motor it) is connected in serieswith a variable resistance carbon pile regulator unit 56 between thebranch conductors 52 and 55.

The armature windings 22 are also in parallel circuit with a solenoidcoil 5'7 and a rectifier 53, the latter of which is arranged to preventenergization of the solenoid coil from the battery power source torequire its energization by back electro-inotive force developed fromthe motor rotating in one direction, while having a reversing currentimpressed across its field windings. The motor armature is connected, asillustrated, to power supply conductor 31 over conductor 59, while thesolenoid coil 57 and rectifier 5a; are arranged in parallel circuittherewith by means of conductor 6d. Conductors 59 and 6t) are joined tothe parallel circuit conductors 52 and 55 over a common conductor nil,while conductors 52 and 55 are in turn joined to the supply lineconductor 42 and the other side of the battery by means of conductor 64.

A power circuit line fuse 65, typically 300 amps, a control circuit fuse66, typically amps, and a key operated ignition switch 67 are alsoincluded in line conductor 42, as shown.

In addition to the aforedescribed elements, the electrical controlcircuitry also includes a parallel circuit conductor 76 extendingbetween line conductors 31 and 5-2 to join a second micro-switch 71, anormally open pressure switch 72, and a relay coil 73 in series circuitelationship. When energized, coil 73 serves to close a set of contacts'74 connected, by conductor '75, in parallel circuit relationship withthe carbon pile regulator 56 and arranged to bypass the regulator 56 anda low speed portion 76 of the motor field windings 21, thus to short outthe resistor and approximately half of the motor field for high speedoperation of the vehicle, as will be amplified hereinafter.

Rotational direction of the drive motor 2% is controlled by thedirection of the current flowing through the field windings asdetermined by the positioning of the direction selector lever and switchblade 2-4 which closes circuit with either the forward or reversedirection switch contacts or 26. The motor 2i) is energized and as aresult the vehicle is, therefore, driven in a forward direction if thecontact sets 5d and 54- are closed simultaneously. in such condition,current flows from the battery 36 over conductors 31 and 53*, motorarmature 22, conductors ll and 52, closed reverse direction contactsEli, the carbon pile regulator 56, motor field windings 21, closedforward direction contacts in conductor 55, and over conductor 64 toline conductor 42 and the other side of the battery. To reverse therotational direction of the motor, contact sets 51 and 53 are closedsimultaneously so that current flows between the battery conductors 3iand 42 over conductor 59, arr iature 22, conductors 611 and 55, closedforward direction contact 53, field windings 21, the carbon pi eregulator 56, closed reverse direction contac. 5i, and conductor 64 tothe other side of the battery and line conductor In order to closeeither contact sets 51 or the direction selector lever and switch bladeof the direction control switch 23 must be engaged with the relateddirection contacts 25 or 26. it wil be understood that the relay coil 39controls the opening and closing operation of the contact sets 32, 53,and 5d, while relay coil 41 controls operation of the reverse dire tioncontact sets 34, 5 and $3.. Therefore, in order to energize the motorfail in a forward direction of rotation, for example, the relay coil 39must first be energized before the relay contacts 5?- can be opened andcontacts closed.

To accomplish this function, the ignition switch s7, the

eat interlock switch 54, and the normally closed microswitch contacts 33must be closed. Movement of the direction selector lever to engage theforward direction contact establishes an energizing circuit throughconductor 36, contacts 33, switch blade 24 conductor 38, coil 39,conductor 33*, and seat switch to the other side of the battery andconductor Upon cnergization of the coil 39, normally open contacts 32and are closed and the normally closed contacts are opened. As pointedout previously, closing contacts 3-2 establishes a hold circuit, so thatsubsequent interruption or opening of the micro-switch contacts 33 willnot result in deenergizing the forward direction coil in a like manner,the reverse dir ction coil i is en: ergized over conductor 236, closednu iO-SWitCll contacts 33, switch blade 24-, reverse direction switchcontact 26, conductor 4%, conductor :13, interlock switch contacts 44,line conductor and the ignition lcey switch 67. Again, upon energizationof the reverse direction coil 4-1, both sets of reverse directi ncontacts 34- and Si are closed and the normally closed reverse directioncontacts 5d are opened. Contacts 3- 2 estab lish circuit over conductor3'7 to hold relay coil ll en ergized after micro-switch contacts 33 areopened.

Speed of the motor is controlled in both the forward and reverse driveconditions, as above described, by changing the pressure applied to thecarbon elements of the variable resistor or carbon pile regulator 56.This results in varying the resistance offered by such regulator 56 andaccordingly adjusts the flow of current to the motor. Such a carbon pileregulator further pro vides infinite variation in speed control for themotor to thereby desirably produce step-less acceleration anddeceleration control of the vehicle in both the forward and reversedirections. When the carbon elements of regulator 56 have beencompressed a predetermined amount, contacts 74 may be closed to shortout the regulator and the low speed motor field windings 76. The closingof the contacts 74 is conditioned, however, on the energizing of therelay coil '73 therefore which is determined by closing the secondmicro-switch contacts 71 and the pressure switch contacts '72, thelatter of which are associated with the hydraulic control means utilizedfor applying pressure to the carbon pile regulator 55, as will now bedescribed.

Turning now to the features and organization of hydraulic control meansemployed for regulating the compression of the carbon pile regulator 5'6in the above described electrical circuit, reference is made to i 'GURE3 of the drawings. it will be understood from FIGURE 3, that a pivotallymovable accelerator pedal associated with the vehicle 1% in aconventional manner, is arranged to operate piston fill of a masterhydraulic cylinder 82 through a suitable actuating linkage arrangement,indicated generally by numeral 33.

Linkage 83 includes a first lever arm which is slidingly engaged at itsouter end by the underside of the foot operated pedal and is attached atits other end to a horizontal pivot axle 85 so that arcuate movement oflever lid rotates aide Axle also has rigid connection with a secondlever arm extending outwardly therefrom to overlie the upper end of thpiston rod 81. A leaf spring element 8'7 is interposed etweenthe leverarm 86 and the piston rod to hold the accelerator pedal in a raisedcondition until such is depressed by the operator. Spring 87 also servesa secondary purpose, in that its initial llexure or depression isrequired before the secondary lever engages the upper end of the mastercylinder piston rod t This provides a limited lost-motion connection,requiring a corresponding limited lost-motion depression of theaccelerator pedal before piston til is moved.

Such lost motion of the accelerator pedal is utilized to actuate anoperating plunger 88 of the microswitch 33 through an operating finger89 depending from the pivot shaft 85. With this arrangement, thenormally closed microswitch contacts 33 may be opened or actuated withinthe lost motion or initial depression action of the accelerator pedal 8%and before piston is moved. Depression of the accelerator pedal beyondits lost motion limit actuates piston 81. Full depression of theaccelerator pedal further engages finger with the operating plunger ilassociated with the second micro-switch 71, so that the same is closedonly when the accelerator pedal is fully depressed or substantially so.

Pressure on the accelerator pedal bit is transmitted to the masterhydraulic cylinder 82 and thereat transformed into hydraulic pressurewhich is transmitted by a suitable conduit and a related piping systemto one end of a fixed carbon pile regulator 56. The transmission ofhydraulic pressure to the carbon pile regulator nay take place overeither one of two hydraulic branch circuits, labeled generally 96 and 97and which branch outwardly from the main supply conduit 95 over aT-connection $55 therein.

The first branch system as includes a conduit and serves hydraulicaccumulator lltll which is designed to momentarily store the hydraulictluid or oil of the closed circuit system in the event that theaccelerator pedal is depressed too rapidly, for instance.

The second branch circuit 9'7 normally serves to operate the regulatorand includes an adjustable needle or orifice valve 1-135 and a solenoidvalve designed to stop the ilow of fluid through the branch in responseto energization of solenoid coil Oil passing through the solenoidoperated valve 1% is transmitted directly to a pressure switch and fromthere by conduit iii? to a hydraulic actuator comprising a piston andcylinder arrangement lib, which has an actuator piston rod illsurrounded by a minimum pressure spring 112 and connected to a shielddisc or plate Trill. Plate 113, in turn, abuttingly engages a ceramicinsulator lid designed to transm t axial compressive force to the carbonpile regulator The actuator circuit 97 also includes a bypass branchline 115 containing a one-way check valve 115 adapted to bypass theorifice or regulator valve 195, solenoid operated valve and the pressureoperated switch Check valve permits prompt return iiow oi. hydraulicfluid to the master cylinder, so that byor ilic pressure in the actuatorand accumulator may be relieved coincidental with the removal of theoperators foot from accelerator pedal Eli and release of the mastercylinder piston Sll.

In addition to the hydraulic force transmitted to the carbon pileregulator through the normal operation or" the actuator lit) and thehydraulic branch circuit 97, compressive force may also be applied tothe carbon pile regulator by the accumulator Till in certain operationcircumstances. This is accomplished through a pivotal linkage arm whichmoves about pivot center and is engaged at one end by the pistonactuator rod 122, of the accumulator 1631, the latter of which comprisesa cylinder and piston arrangement wherein hydraulic pressure transmittedto the accumulator circuit works the iston against a return spring, allin conventional and known manner. A leaf spring 123 is fixed at itslower end to the accumulator actuated lever 12% and engages the shieldplate 113 at its upper end adiacent the same area where such shieldplate is connected to the piston rod llllll. It will be understood thatwith this arrangement fluid applied to the accumulator, as for example,when the solenoid valve Hi6 is clo d, will be transmitted as hydraulicpressure and act directly through the lever 123 and spring E2? tocornpress carbon pile regulator 55. In this respect, it should berecognized that the maximum force which the accumulator may apply to thecarbon pile unit is limited by the force which the flexible leaf spring123 is capable of transmitting.

Having thus outlined the hydraulic system which applies compressiveforce to the carbon pile regulator, the specific operating features andpurposes of the various elements embodied therein will now be discussed.To this end, the actuator circuit 97 will first be considered.

The needle valve of the actuator circuit Q7 effects a predetermined timedelay or rate of fiow for the hydraulic fiuid, so as to produce a giventime limit for the actuator lid to compress the carbon pile unit "6 withmaximum hydraulic pressure. This, therefore, limits the rate ofacceleration for the vehicle.

The solenoid valve tilt? is operable only at the energization of thesolenoid coil 57, which in turn is energized by the back EMF. of l hemotor, the solenoid valve closing to disrupt the flow of pressurizedfluid to the actuator over the circuit 97. These operating conditionsfor solenoid ltl reveal that energization of solenoid coil from the backEMF. of the motor is possible only in those instances of motor operationwhere the armature is r t-ating in a direction opposite to therotational sense required by the how of electric current through thfield windings. This occasion arises, for instance, upon quick reversalof the direction selector switch, as when the vehicle is going forwardand it is desired to reverse its direction. In such instances, movementof the direction selector switch to engage the reverse direction switchcontact 26, immediately disrupts the circuit through the forwarddirection relay coil 39, opening contacts 32 and and closing contacts53. it will be recalled that before the reversing current can be appliedto the field windings, however, the reversing contacts ill must beclosed and contacts 58 open. in order LO open contacts and closecontacts 51 it is necessary to energize the reverse direction relay coil41. This would be possible by the direct movement of the switch blade 23from the forward contact 25 to engage reverse contact 26 if it were notfor the fact that in so moving th switch blade, the same acts as acircuit interrupter or line switch to deenergize the control circuit.Thus, when blade 23 engages the reverse contact as, coil fails toenergize until circuit is established from the supply conductor 31 tothe blade Such circuit may be established over the micro switch contacts33, but which are closed only when the accelerator pedal is raised torelieve pressure on the master cylinder and the hydraulic circuit. Byraising the accelerator pedal to close contacts 33, reversing coil 41 isenergized to close contacts 34 and 5d, and open the normally closedreverse direction contacts This energizes the motor field windings forreverse direction operation.

l f the armature .22 is then rotating in a forward direction, a backEMF. is present to energize the solenoid coil 57 through rectifier 58which permits current flow in opposition to battery current, therebyclosing solenoid valve 166. When this happens, the flow of fluid in thehydraulic circuit 97 is cut oil and transmitted to accumulator lilll.

It will be recognized that depression of the accelerator fill, with thesolenoid valve closed, places the accumulator in direct circuit with themaster cylinder as above described. The accumulator acts as a secondaryactuator to compress the carbon pile regulator throug lever and spring123 thus varying the carbon pile regulators resistance in the motorcircuit to vary 7 the reverse braking torque in response to thehydraulic pressure applied by accelerator pedal operation.

Thus, variable deceleration control for the vehicle is provided, suchcontrol being infinitely variable in accordance with the compression ofthe carbon pile regulator. Preferably, the maximum permissible reversetorque braking which may be applied is just slightly less than thatwhich would deceierate the vehicle suiiiciently to lose a load beingcarried on the lift fork 13. This is to sea, the braking torque appliedthrough the manipulation of the accum rlator, as above described, islimited to a mum determined by the force capable of being transmitted byleaf spring 123, this maorimum being productive of a safe rate ofdeceleration for the vehicle, which is predetermined to be less thanthat required to throw or slide a load 053 the lift forks id. Thecontrolled reverse torque braking is also limited to a minimum valuedetermined by the dorce applied by the in um cressure spring 112,associated with the actuator ll l. Between such minimum and maximumlimits, the braking torque is infinitely variable, as above discussed,in accordance with the hydraulic pressure produced at the mastercylinder The solenoid valve res, in conjunction with the microswitch 33,also serves as an antiplugging interlock for preventing the applicationof the full battery load across the motor when the armature 2% isrotating in an opposing direction. This is so since it is necessary forthe operator to remove his foot from the accelerator pedal to closemicro-switch contacts before the direction relay coils 39 or may beenergized to close the forward or reverse direction contac'tors; untilsuch direction contact sets 51 or 5 1- \are closed, the motor 23* cannotbe energized. Thus, plugging in the sense of applying full battery powerto the motor in reverse sense to the rotational direction of itsarmature is effectively prevented, yet controlled reverse torque brakingis permitted, as above discussed.

The pressure switch "72 provided in the hydraulic circuit 97 is adjustedto close its contacts at a pressure just below the maximum systempressure, as produced by the maximum depression Otf the ccelerator pedalClosing of the pressure switch contacts thus would normally occur priorto depressing the accelerator pedal sufii lent to opcrate the secondmicro-switch '71. Then closing of the latters contacts permitsenergization of the relay coil '73 to close its related contactor 74,thereby shunting the carbon pile regulator and the low speed fieldwinding '76 of the motor. When this happens, the truck is conditionedfor high speed operation. The pressure switch '72 guarantees thatshorting out of the carbon pile regulator will not occur, however, eventhough the accelerator pedal be fully depressed to energize the secondmicrowitch 71, until a desired hydraulic pressure has con acl'u'eved inthe hydraulic actuator system; deternined by the regulator needle valveThis feature insures full compression of the carbon pile regulator toits minimum resistance value before the same is shunted out of the motorcircuit.

The ch ck valve 116 in bypassing ranch 5 permits free flow return of thepressurized fluid in the actuator lltl to the master cylinder 82 andaccumulator lfill, by bypassing the restricting needle valve Hi5. Suchimmediate relief of the hydraulic pressure in the actuator serves toaccordingly decompress the carbon pile regulator and increase itsresistance to maximum value. The checic valve, therefore, enters intothe anti-plug feature, above discussed, performed by the solenoid valveand the micro-switch contacts 33. it will be understood in this respectthat the check valve guarantees that the hydraulic energy stored in theactuator cylinder will not continue to operate the carbon pile afterenergizing the field windings in reverse to the armatures rotation. l tprompt relief of fluid pressure from the actuator, such as isaccommodated by the checn valve lid, were not provided for, pluggingcould occur upon energizing a reversing direction circuit, sincepressurized fluid might be rapped in the actuator and continue to holdthe carbon pile regulator in a compressed condition, in which conditiondie regulator would impose little resistance the field winding circuit.In the illustrated embodiment of the invention, this plugging conditioncould continue until the needle valve ltlfi had permitted the pressurestored in actuator to bleed oil, which would require a significantperiod of time during which the solenoid valve could be closed, in whichlatter event, the actuator might remain hydraulically locked in aregulator compressing condition. The capacity or" the bypass circuit forimmediate relief of fluid pressure from the actuator, together with thenecessity for the operator to release the accelerator pedal in order tocheer motor rc- 'versing, thus assures against 'a plugging" condition.

From the foregoing, it is believed that those familiar with the art willreadily appreciate the improved features for operating a carbon pileregulator afforded by the hydraulic control system of this invention. inparticular, it is significant that an etlcctive interlock against fullcurrent plugging is provided, while permitting, within predeterminedlimits, an effective and infinitely variable, reverse torque ibrakingcontrol of the motor through the operation of the hydraulic accumulatoras a secondary actuator. it will be understood also that the provisionof a hydraulic actuator circuit provides rfor stepless speed variationand simplified control of the carbon pile regulator, directly by theoperator, while the needle valve ltlz": requires a predetermined timedelay in applying the full compressive force to the carbon pileregulator. The check valve lilo permits free return flow of thehydraulic lluid to also prevent plugging by virtue of accumulatedpressure energy in the actuator. The micro-switch 33, operated onlywithin initial depressing movement of the accelerator pedal, joins withsuch check valve and the solenoid operated valve 1% to prevent theapplication of full battery load to the motor in reverse to eitherforward or reverse direction motor operation, when the carbon pileregulator is compressed to a minimum resistance condition. It will alsobe understood from the foregoing that the lever operated directionswitch acts as line interrupter in the control circuit at the change ofselected direction. This feature operates to deenergize the forward andreverse relay coils and contacts and resultingly requires closing of themicro-switch contacts before a reversing circuit for applying energy tothe field windings, contrary to the rotational direction of thearmature, may be energized. This further guarantees against lull currentplugging of the motor.

While the foregoing description sets forth the principal features andoperational advantages of my improved invention, a regulat ry adjustmentto accommodate linear or rial expansion and contraction or" the carbonpile regulator due to operational temperature change is desirable, sincea movement of the carbon pile relative to the actuator piston illeffectively alters the force ca ble of eing applied to the carbon pileregulator for a given value of hydraulic pressure in the actuator. inorder to compensate for this factor, automatic compensator means isincorporated in the hydraulic actuator As seen in FIGURE 4, actuatorincludes a twopart housing having a first shell portion 1 .35; whichencloses a hydraulic chamber 131 and a second shell portion abuttinglyengaged with the first shell portion to enclose an air ch c oer Thehydraulic chamber 131 has a thydr ulic fluid inlet 13 1-, while airchamber T133 vents to atmosphere.

A cup-shaped piston assembly is movable in and between the two chambersand 133 in response to the application of pressurized fluid on thehydraulic side of a flexible diaphragm which is attached to the pis-11;)! ton assembly 135 and is sealed at its outer periphery between thetwo shell portions 139 and 1 32 by plural holding bolts 13%. The pistonassembly 135 includes a cupshaped piston member 13% movable towards airchamher 133 against a return spring 1 th. The piston 13% is supportedconcentrically Wit in the housing portions llBll and and engages theouter periphery of an annular CE-ring seal i l-it held in an annularrecess of a plunger supporting threaded collar, extending axiallythrough a central opening of the piston The return spring li isconcentrically supported within the cup-like piston and surrounds acylindrical guide sleeve res which is brazed atone end in a suitableopening formed in an outer end wall il l6 of the housing shell 132. Theguide sleeve is formed with a central axial bore into which a tubularpiston 15% is fitted for sliding movement. Piston has a reduced portion151 at its outer end disposed concentrically inward of the minimumpressure spring ill/2. The axially innermost end of the mini-rerunpressure spring ll ii abuts one of a number of annular spacer members152 mounted concentrically about the tubular piston and surrounding acylindrical shoulder F53. The spacers may be varied in numher and sizeto regulate the zero load compression of spring 1312, thereby adjustingits minimum pressure engagement with plate T113.

The tubular piston is also formed with a central axial chamber bore 155which receives the actuator piston ill; the latter being connected tothe shield plate lllffi by a screw member 156. An annular recess isvided adjacent the inner end of the actuator piston for housing anannular il-ring seal and such provides an oil tight seal between thepiston and the side walls of chamber bore 11555. The axially innermostend of the tubular piston 155) a uts a washer which is disposed on thebottom wall of the diaphragm actuated piston 1 9. Tubular piston moveswith the cup-shaped piston the latter serving to compress return spring14%, While the piston 15d compresses the minimum pressure spring 112.

T e collar M3 is threaded into an axial bore formed inwardly of theleft-hand end of the tubular ton (see FEGURE 4) and communicatingcoaxialiy with the ch n or bore 155, while a pilot plunger sea isdisgiosed wi iin an axial pilot chamber bore 163 of the collar. PlungerM2 is surrounded at one end by a compression spring 164 which serves toreturn the pil plunger to the left, as seen in FlGURE 4. Spring isengaged at one end by an enlarged annular shoulder of the plunger and atits opposite end by an annular Washer 166 mounted over the inner end ofthe axial bore 15s. The pilot plunger includes a reduced cylindricalneck portion adjacent its axially outermost and a pilot extension 169 atits axially innermost end. The pilot extension passes through the Washerlied and serves thereby to guide the plunger in chamber An il -ring sealll'tl surrounds the neck portion res to effect a seal with the adjacentface of shoulder and a shoulder face 171 at the bottom or inner end ofthe pilot chamber Front examining FIGURE 4, it will be recognized thatneck nortion rides in a cylindrical bore of the and is integral with aportion 175 which extends an ally therefrom and through a small bore7.76 in the colar to project axially outward oi the latterx Fingerportion 1175 is intended to periodically engage an adjustable stopcarried coaxialiy within a stop bushing 83 fixed to the end wall 182 ofthe housing shell portion 136? and an annular (B-ring seal 18 i isprovided to prevent the escape of pressurized fluid from the hydraulicchamber 131 past the stop member. The stop i) is adjustable in therespect that it may be adjustably moved toward away from the finger ofthe pilot plunger along a bore in which it is mounted. The stop normallyengages the pilot inger when the hydraulic pressure is relieved fromchamber 131 so that re turn spring l may force head portion of the pilotcollar into abutting engagement with the stop bushing i in this regard,it will he noted that the collars head 1Q portion is suitably slotted at187 to provide communication between the fluid chamber and the axialbores therein.

With the above-described arrangement, fluid under pressure directedthrough the inlet port will cause the piston to move to the right, asviewed in FlGURlE 4, compressing the return spring and permitting theSuing to perform as a as it is pressed against the adjacent faces of theenlarged shoulder portion 355 of the pilot plunger and the bottom Wallor shoulder 171 of the oilot collar chanrbc so. Hydraulic fluid withinthe pilot piston chamber and the bore 155 which houses the actuatingpiston all is thereby effectively locked between the Qiing seals iSS andHi), so that the hydraulic force exerted on the piston assembly H5 is.ittcd directly to the carbon pile resistor through ti o actuator pistonWhen the operator rernoves his foot i am the accelerator pedal, however,this relieves the hydrauli pressure of the closed hydraulic circuit, andthe piston ass 'nbly is returned to the left, as viewed in El- URE 4,lllldc' iuence of the return spring This acti "y event "rigs the fingerportion 175 of the pilot plunger into engage. eat with the adjustablestop i o, moving the (bring i out of sealing engagement with theadjacent shoulder in the pilot plunger chamber Since the fi wit in thehydraulic chamber is in corn iunication with the (E-ring seal by way ofthe slotted openings i8? in the h ad of the collar member 1 r and thespaci around the plunge portions y understood that hydraulic veen thefluid chamber and enevcr tit-ring lii) is unseatcd. occurs, as abovenoted, every r removes his foot from the accelerator pressure of the inof the hydraulic 1 o ircuit to zero or a rnininnun value.

Such ati of the fluid in the lockup chamber en the i A regulator. Thus,if the length or has grown or increased, the pressure of the fiuidbetween the tD-rings and l'l'il will be greater 4 l Therefore,tins-eating of G-ring ti n that in cha nocr it Wil permit the escape ofsufficient amount of fluid he pilot plunger and into chamber to provideinovenent of the actuating piston relative to t lar piston and axiallytoward the pilot plunger. On the other hand, it the carbon pi eregulator has dec n ng the ini \rn pressure spring vill ht, toward thecar- URE 4, when the actuator pressure is relieved. i then .aces thelockup 0 author between t e G- i and I, under an effective vacuum, sothat when (Bring Wil is unseated, such lockup chamber is s d withadditional hydraulic fluid from the Chan e actuator.

From the foregoing, it is believed that those familiar with the art willreadily understand and appreciate the novel is turcs and advantageswhich the present invent'on presents. is further to be understood thatwhile I have herein shown and described the features and conccnts of nayinvention as they are related to the operation and control of an indust-ial lift truck, such area or" use is by no means to be considered arestrictive limitation on the scope of my invention. Also, it will beappreciated that numerous changes, modifications, and substitutions ofequivalents may occur in the carticular apparatus and control systemshercinaoovc described without necessarily eparting from the spirit andscone of invention. As a consequence, it s not my intention to belimited to the particular embodiment herein shown and described, excentas may appear in the following appended claims.

1 claim:

1. In control means for a vehicle having an electric rcgtnator, as seenin F drive motor, a pressure responsive carbon pile regulator forsteplessly varying the flow of electric current to said motor thereby touniformly regulate its rotational speed, forward and reverse directionselector switch means electrically controlling the motors direction ofrotation continuously operable hydraulic control means inclu g hydraulicactuator means effective for continuously increasing and decreasing thepressure exerted on said regulator means by said hydraulic control meansand hydraulic accumulator means operatively associated with saidregulator, and means re ponsive to baclr EMF. of said motor forisolating said actuator in said control system and for rendering saidaccumulator means operative to compress decompress said regulator herebyselectively to control deceleration of said motor.

2. In control means for a vehicle having an electric drive motor, acarbon pile regulator means for steplessly adjusting the rotationalspeed of the motor, a hydraulic control circuit including a continuouslyoperable hydraulic actuator for axially and continuously exertingvariable pressure on said regulator to selectively adjust its resistanceand the rotational speed of the motor, an accumulator in said controlcircuit, an accelerator pedal for varying hydraulic pressure in saidcontrol circuit, a direction selection switch for controlling therotational direction of the motor, electrical interlock meansoperatively responsive to the actuation of said accelerator pedal andrequiring relief of pressure on said regulator prior to the energizationof said motor in a sense reverse to the direction of rotation for itsarmature, electrically controlled valve means in said control circuitoperable in response to counter EMF. of the motor for stopping flow ofhydraulic fluid to said actuator, and means operated by said accumulatorfor selectively compressing and decompressing said regulator in responseto manipulation of said accelerator pedal when said valve means isoperated.

3. The combination :as set forth in claim 2 in which there is also meansin said hydraulic circuit operable independently of the manipulation ofsaid accelerator pedal for controlling the rate at which said regulatormay be compressed by said actuator.

4. The combination as set forth in claim 2 in which there is also aswitch means operable by the manipulation of said accelerator pedal forshunting said regulator to condition the motor for high speed operation.

5. The combination as set forth in claim 2 in which there is also apressure switch means responsive to a predetermined hydraulic pressurein said control circuit for shunting said regulator to condition themotor for high speed operation.

6. The combination of claim 2 in which there is also additional meanscompensating for the thermal axial expansion and contraction of saidregulator.

7. in control means for a vehicle having an electric drive motor, acarbon pile regulator means for steplessly adjusting the rotationalspeed of the motor, a hydraulic control circuit including a continuouslyoperable hydraulic actuator etfective for axially and continuouslycompressing said regulator to variable extent effective for selectivelyoperating its resistance and the rotational speed of the motor, anaccelerator pedal for varying hydraulic pressure in said control circuitthereby to control the rotational speed of the motor, electric circuitmeans for shunting said regulator to condition the motor for high speedoperation, switch means actuated by said accelerator pedal upondepression thereof for controlling said electric circuit means, meansfor delaying energization of said electric circuit means subsequent toactuation of said switch means upon depression of said pedal, adirection selection switch for controlling the rotational direction ofthe motor, electrical interlock means operatively responsive toactuation of said accelerator pedal and requiring decompression of saidregulator prior to 12 energization of said motor in a sense reverse tothe direction of rotation for its armature, and electrically controlledvalve means in said control circuit operable in response to counter EMF.of the motor for stopping flow of hydraulic fluid to said actuator untilsaid armature slows down to a predetermined speed of rotation.

8. in control means for a vehicle having an electric drive motor, apressure responsive regulator for steplessly varying the flow ofelectric current to said motor to thereby uniformly regulate itsrotational speed, forward and reverse switch means controlling thedirection of rotation of said motor, continuously operable hydraulicmeans operable independently of the speed of rotation of said motor andeffective for selectively and continuously applying variable operatingpressure to said regulator, and interlock switch means in circuit withsaid forward and reverse switch means and interloclcingly operative withsaid hydraulic means effective for assuring release of actuatingpressure from said regulator prior to reversal of the direction ofrotation of said motor responsive to operation of said forward andreverse switch means.

9. In control means for a vehicle having an electric drive motor, apressure responsive carbon pile regulator for steplessly varying theflow of electric current to the field windings of said motor to therebyuniformly regulate its rotational speed, forward and reverse switchmeans selectively controlling the direction of rotation of said motor,continuously opera is hydraulic control means operable independently ofthe speed of rotation of said motor and e--ective for continuouslyapplying variable operating pressure to said regulator, interlock switchmeans responsive to operation of said hydraulic control means forprecluding reversing of said motor prior to release of operatingpressure on said regulator, said interlock switch means being operableindependently of reversing operation of said forward and reversingswitch means, means for regulating the rate at which said hydrauliccontrol means may apply operating pressure to said regulator, and meansfor releasing said regulator from operating pressure preliminary toreversal of the direction of rotation of said motor.

10. In control means for a vehicle having an electric drive motor, acarbon pile regulator for steplessly adjusting the rotational speed ofthe motor, a hydraulic control circuit comprising a continuouslyoperating actuator operable independently of the speed of rotation ofsaid motor and effective for axially and continuously compressing saidregulator to variable extent effective for adjusting its resistance andthe rotational speed of said motor, an accelerator pedal openableindependently of the speed of rotation of said motor for varyinghydraulic pressure in said control circuit thereby to control therotational speed of said motor, electric circuit means for shun-tingsaid regulator for hi h speed operation of said motor, switch meansoperable responsive to operation of said accelerator pedal forcontrolling said electric circuit means, and means for delayingenergization of said electric circuit means subsequent to actuation ofsai switch means.

Reference UNITED STATES PATENT OFFICE CERTIFICATE OF GORECTTQN PatentNo,, 3 ll4 871 December 17 1963 Frank Jo Schenkelberger It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 11 line 9,, strike out 'xrmeans" P first occurrence; line 61 for"operating" read adjusting --o Signed and sealed this 28th day of April1964.

(SEAL) fittest;

ERNEST We SWIDER EDWARD In BRENNER Attesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,3 ll4 87l December 17, 1963 Frank Jo Schenkelberger It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 11, line 9 read adjusting Signed and sealed this 28th day ofApril 1964.

(SEAL) Attest:

ERNEST Wu SWIDER EDWARD J, BRENNER Attesting Officer Commissioner ofPatents

10. IN CONTROL MEANS FOR A VEHICLE HAVING AN ELECTRIC DRIVE MOTOR, ACARBON PILE REGULATOR FOR STEPLESSLY ADJUSTING THE ROTATIONAL SPEED OFTHE MOTOR, A HYDRAULIC CONTROL CIRCUIT COMPRISING A CONTINUOUSLYOPERATING ACTUATOR OPERABLE INDEPENDENTLY OF THE SPEED OF ROTATION OFSAID MOTOR AND EFFECTIVE FOR AXIALLY AND CONTINUOUSLY COMPRESSING SAIDREGULATOR TO VARIABLE EXTENT EFFECTIVE FOR ADJUSTING ITS RESISTANCE ANDTHE ROTATIONAL SPEED OF SAID MOTOR, AN ACCELERATOR PEDAL OPERABLEINDEPENDENTLY OF THE SPEED OF ROTATION OF SAID MOTOR FOR VARYINGHYDRAULIC PRESSURE IN SAID CONTROL CIRCUIT THEREBY TO CONTROL THEROTATIONAL SPEED OF SAID MOTOR, ELECTRIC CIRCUIT MEANS FOR SHUNTING SAIDREGULATOR FOR HIGH SPEED OPERATION OF SAID MOTOR, SWITCH MEANS OPERABLERESPONSIVE TO OPERATION OF SAID ACCELERATOR PEDAL FOR CONTROLLING SAIDELECTRIC CIRCUIT MEANS, AND MEANS FOR DELAYING ENERGIZATION OF SAIDELECTRIC CIRCUIT MEANS SUBSEQUENT TO ACTUATION OF SAID SWITCH MEANS.